In 1755 LeRoy passed the discharge of a Leyden jar through the orbit of a man who was blind from cataract and the patient saw “flames passing rapidly downwards.” Ever since, there has been a fascination with electrically elicited visual perception. The general concept of electrical stimulation of retinal cells to produce these flashes of light or phosphenes has been known for quite some time. Based on these general principles, some early attempts at devising prostheses for aiding the visually impaired have included attaching electrodes to the head or eyelids of patients. While some of these early attempts met with some limited success, these early prosthetic devices were large, bulky and could not produce adequate simulated vision to truly aid the visually impaired.
In the early 1930's, Foerster investigated the effect of electrically stimulating the exposed occipital pole of one cerebral hemisphere. He found that, when a point at the extreme occipital pole was stimulated, the patient perceived a small spot of light directly in front and motionless (a phosphene). Subsequently, Brindley and Lewin (1968) thoroughly studied electrical stimulation of the human occipital (visual) cortex. By varying the stimulation parameters, these investigators described in detail the location of the phosphenes produced relative to the specific region of the occipital cortex stimulated. These experiments demonstrated: (1) the consistent shape and position of phosphenes; (2) that increased stimulation pulse duration made phosphenes brighter; and (3) that there was no detectable interaction between neighboring electrodes which were as close as 2.4 mm apart.
As intraocular surgical techniques have advanced, it has become possible to apply stimulation on small groups and even on individual retinal cells to generate focused phosphenes through devices implanted within the eye itself. This has sparked renewed interest in developing methods and apparatus to aid the visually impaired. Specifically, great effort has been expended in the area of intraocular retinal prosthesis devices in an effort to restore vision in cases where blindness is caused by photoreceptor degenerative retinal diseases; such as retinitis pigmentosa and age related macular degeneration which affect millions of people worldwide.
Neural tissue can be artificially stimulated and activated by prosthetic devices that pass pulses of electrical current through electrodes on such a device. The passage of current causes changes in electrical potentials across visual neuronal membranes, which can initiate visual neuron action potentials, which are the means of information transfer in the nervous system.
Based on this mechanism, it is possible to input information into the nervous system by coding the sensory information as a sequence of electrical pulses which are relayed to the nervous system via the prosthetic device. In this way, it is possible to provide artificial sensations including vision.
One typical application of neural tissue stimulation is in the rehabilitation of the blind. Some forms of blindness involve selective loss of the light sensitive transducers of the retina. Other retinal neurons remain viable, however, and may be activated in the manner described above by placement of a prosthetic electrode device on the inner (toward the vitreous) retinal surface (epiretinal). This placement must be mechanically stable, minimize the distance between the device electrodes and the visual neurons, control the electronic field distribution and avoid undue compression of the visual neurons.
In 1986, Bullara (U.S. Pat. No. 4,573,481) patented an electrode assembly for surgical implantation on a nerve. The matrix was silicone with embedded iridium electrodes. The assembly fit around a nerve to stimulate it.
Dawson and Radtke stimulated cat's retina by direct electrical stimulation of the retinal ganglion cell layer. These experimenters placed nine and then fourteen electrodes upon the inner retinal layer (i.e., primarily the ganglion cell layer) of two cats. Their experiments suggested that electrical stimulation of the retina with 30 to 100 μA current resulted in visual cortical responses. These experiments were carried out with needle-shaped electrodes that penetrated the surface of the retina (see also U.S. Pat. No. 4,628,933 to Michelson).
The Michelson '933 apparatus includes an array of photosensitive devices on its surface that are connected to a plurality of electrodes positioned on the opposite surface of the device to stimulate the retina. These electrodes are disposed to form an array similar to a “bed of nails” having conductors which impinge directly on the retina to stimulate the retinal cells. U.S. Pat. No. 4,837,049 to Byers describes spike electrodes for neural stimulation. Each spike electrode pierces neural tissue for better electrical contact. U.S. Pat. No. 5,215,088 to Norman describes an array of spike electrodes for cortical stimulation. Each spike pierces cortical tissue for better electrical contact.
The art of implanting an intraocular prosthetic device to electrically stimulate the retina was advanced with the introduction of retinal tacks in retinal surgery. De Juan, et al. at Duke University Eye Center inserted retinal tacks into retinas in an effort to reattach retinas that had detached from the underlying choroid, which is the source of blood supply for the outer retina and thus the photoreceptors. See, e.g., E. de Juan, et al., 99 Am. J. Ophthalmol. 272 (1985). These retinal tacks have proved to be biocompatible and remain embedded in the retina, and choroid/sclera, effectively pinning the retina against the choroid and the posterior aspects of the globe. Retinal tacks are one way to attach a retinal electrode array to the retina. U.S. Pat. No. 5,109,844 to de Juan describes a flat electrode array placed against the retina for visual stimulation. U.S. Pat. No. 5,935,155 to Humayun describes a retinal prosthesis for use with the flat retinal array described in de Juan.
In U.S. Pat. No. 6,743,345 “Method of Metallizing a Substrate” to Christian Belouet et al. a process for metallizing a substrate is disclosed, comprising coating the part with a precursor composite material layer consisting of a polymer matrix doped with photoreducer material dielectric particles; irradiating the surface of the substrate with a light beam emitted by a laser; and immersing the irradiated part in an autocatalytic bath containing metal ions, with deposition of the metal ions in a layer on the irradiated surface, and wherein the dimension of the dielectric particles is less than or equal to 0.5 μm. The process includes three steps. The first step is to coat the substrate part with a precursor composite material layer consisting of a polymer matrix doped with photoreducer material dielectric particles. The second step is to irradiate the surface of the substrate with a light beam emitted by a laser. The third step is to immerse the irradiated part in an autocatalytic bath containing metal ions, with deposition of the metal ions in a layer on the irradiated surface, wherein the dimension of the dielectric particles is less than or equal to 0.5 μm.
In U.S. Pat. No. 5,599,592 “Process for the Metallization of Polymer Materials and Products Thereto Obtained” to Lucien D. Laude a positive metallization process for metallizing a polymer composite piece containing a polymer material and oxide particles is disclosed, the oxide particles being made of one or more oxides, comprising three successive steps. The first step consists of the irradiation of a surface area of a polymer piece to be metallized with a light beam emitted by an excimer laser. The polymer piece is made from a polymer material and oxide particles. The oxide particles are made from one or more oxides. The second step consists of immersing the irradiated polymer piece in at least one autocatalytic bath containing metal ions. The immersion induces the deposit of the metal ions onto the irradiated surface area to form a metal film on the surface area, resulting in the selective metallization of the surface area of the polymer piece. The third step consists of thermally processing the metallized polymer piece to induce diffusion of the deposited metal film into the polymer material of the polymer piece. The disclosure of U.S. Pat. No. 5,599,592 is incorporated herein by reference.
Lucien D. Laude et al. report that excimer lasers are effective tools in engraving ceramics and polymers, changing irreversibly the surface of the irradiated material, and restricting these effects to specific areas of interest. See L. D. Laude, K Kolev, Cl. Dicara and C. Dupas-Bruzek “Laser Metallization for Microelectronics for Bio-applications”, Proc. of SPIE Vol. 4977 (2003), pp 578-586.
In U.S. Pat. No. 5,935,155 “Visual Prosthesis and Method of Using Same” to Mark S. Humayan et al. it is disclosed a visual prosthesis, comprising means for perceiving a visual image, said means producing a visual signal output in response thereto; retinal tissue stimulation means adapted to be operatively attached to a retina of a user; and wireless visual signal communication means for transmitting said visual signal output to said retinal tissue stimulation means.
In U.S. Pat. No. 6,878,643 “Electronic Unit integrated Into a Flexible Polymer Body” to Peter a. Krulevitch et al. it is disclosed a method of fabricating an electronic apparatus, comprising the steps of providing a silicone layer on a matrix, providing a metal layer on said silicone layer, providing a second layer of silicone on said silicone layer, providing at least one electronic unit connected to said metal layer, and removing said electronic apparatus from said matrix wherein said silicone layer and said second layer of a silicone provide a spherical silicone body.
J. Delbeke et al. demonstrate that silicone rubber biocompatibility is not altered by the metallization method. See V. Cince, M.-A. Thil, C. Veraart, I. M. Colin and J. Delbeke “Biocompatibility of platinum-metallized silicone rubber: in vivo and in vitro evaluation”, J. Biomater. Sci. Polymer Edn, Vol. 15, No. 2, pp. 173-188 (2004).
All of these soft polymer arrays approximate the shape of neural tissue, particularly the retina. However, there is a need for an improved means for attaching an electrode array to neural tissue and, thereby, improving the array's ability to conform to the neural tissue.